Sealed-in contact structure with extended glow discharge surfaces



April 6, 1965 BORCHERT ETAL 3,177,328

SEALED-IN CONTACT STRUCTURE WITH EXTENDED GLOW DISCHARGE SURFACES Filed July 20, 1960 HI Mil i Fig.3

United States Patent Office 3,177,323 SEALED-1N CONTACT STRUCTURE WiTi-i EX- TENDEE) GLQW DETIHARGE SURFACES Lothar liiorchert, Haar, near Munich, Christian Huber,

Munich-Satin, and Kari-Ludwig Ran, Munich, Germany, assignors to Siemens 8: Halshe Aktiengeseilschaft, Berlin and Munich, a corporation of Germany lFiled .inly 20, 1960, Ser. No. 44,1? Ciaims priority, application Germany, Aug. 6, H59, S 64,319 3 iaims. (Cl. 2till166) This invention is concerned with a sealed-in contact structure comprising highmelting contact means.

A sealed-in contact structure comprises magnetizable contact springs disposed within a glass tube which is hermetically fused at its ends. The glass tube may be filled with a protective gas, for example, a mixture of nitrogen and hydrogen, to prevent corrosion of the contacts. The same effect is obtained by filling the giass tube with a noble gas, for example, argon. Accordingly, such a structure constitutes in principle a contact arrangement disposed within a hermetically sealed chamber which is filled with a protective gas or a noble gas.

The object of the present invention is to considerably increase the life of such contact structures. In accordance with the invention, this object is realized by the provision of means, at the areas of the contacts over which a glow discharge extends upon contact actuation, forming a surface of a highmelting metal, for example, molybdenum, tungsten, tantalum, acting in the manner of a pure metal cathode.

The invention is based upon recognition of the following observations: The contact springs of a contact structure, assuming that they are disposed in a gas atmosphere, may be compared with the electrodes of a gas discharge tube. Accordingly, a glow discharge will occur between the electrodes during the opening operation thereof in the presence of a voltage thereon which exceeds the firing voltage. This occurs especially when an inductive load, for example, a relay, is to be switched by means of such a contact structure. In such a case, the spontaneous current interruption elfects induction of a voltage peak appearing directly at the contact gap and thereby firing the glow discharge.

The consequence is a vaporization of the contact parts forming the cathode, the so-called cathode vaporization, showing itself in wear of the corresponding surface part and in migration of the material, which have a most unfavorable eifect on the properties of the contact points.

There are certain metals known, namely, metals with relatively high melting point, for example, molybdenum, tungsten or tantalum, which oifer a very high resistance to the cathode vaporization occurring incident to glow discharges. Such metals have already been used in cathode tubes in connection with so-called pure metal cathodes. However, these metals appeared until now unsuitable for contact materials because experience with such contacts, operated in air, for example, tungsten contacts, showed that these materials tend, especially with weak loading, toward formation of high resistance layers and even insulating layers. The contact springs of sealedin contact devices therefore have usually been provided with a noble metal layer or coating, for example, gold, which is however less resistant against cathode vaporization.

The above noted highmelting metals such, for example, as molybdenum, tantalum or tungsten, employed as surface materials of contact springs disposed in a hermetically sealed chamber or space filled with a protective gas or noble gas, make it possible to practically eliminate the 3,177,328 Patented Apr. 6, 1965 detrimental cathode vaporization; the otherwise observed tendency of such metals, to form high resistance layers or coatings being thereby prevented by the protective gas or noble gas.

The above described measures taken in accordance with the invention result in long life of the contacts since undesired alteration thereof, due to glow discharge, is largely eliminated. This also results in an improvement with respect to the time constants of the electric and magnetic characteristics. In accordance with an advantageous embodiment of the invention, the highmelting metal is provided upon the contact springs in the form of foils.

The various objects and features of the invention will appear from the description thereof which is rendered below with reference to the accompanying drawing, in which FIG. 1 shows an embodiment of a sealed-in contact device or structure according to the invention with the highmelting metal secured to the contact spring in the manner of foils; and

FIGS. 2 and 3 illustrate an embodiment in which the highmelting metal is riveted to a contact spring.

In FIG. 1, numeral it indicates the sealing or protective tube containing the contact springs 2 and 3. The tube 1 is made of glass and is fused at its ends about the contact springs 2 and 3. The contact springs 2 and 3 are within the contact points or areas thereof provided each with a foil 4 consisting of a highmelting metal, for example, molybdenum. As is apparent from the drawing, the foil 4- is drawn about the respective contact springs 2 and 3 so as to produce relatively large areas which are adapted to otter a correspondingly high resistance against cathode vaporization incident to a glow discharge occurring in operation of the structure. It is, of course, possible, in the event that large cathode surfaces are to be expected, to draw the foils 4 over the entire areas of the respective contact springs 2 and 3 extending into the interior space of the protective tube 1. 7 Another possibility of providing the contact springs with the metal forming the highmelting surfaces, is to arrange such metals in the form of rivets of suitable configuration. Such a structure is shown in FIG. 2 in elevation and in FIG. 3 in part sectional view.

As will be seen from FIGS. 2 and 3, the rivet 5 has a dish-shaped part disposed on a spring such as indicated at 7, facing in the direction of the other spring (not shown) cooperating therewith. The stem 6 of the rivet extends through the contact spring 7 and is riveted over on the other side of the contact spring as shown. This embodiment sufiices for cases in which the contacts are subjected to relatively slight current loads.

Both contact parts belonging to a contact structure are advantageously provided with a highmelting metal. Such a contact structure can be connected in a circuit regardless of the direction of the current to be controlled while at the same time considerably reducing the so-called finemigration emanating from the contact spring representing the cathode.

In accordance with another feature of the invention, the operative effect of the above described measures may be supported or enhanced by filling the hermetically sealed space, containing the contacts, with a gas at a pressure which is as compared with the atmospheric pressure reduced to such extent that a glow discharge will extend with its cathodic coverage over an area which is considerably larger than the contact area belonging to the contact points, so that the cathode vaporization caused by the glow discharge is preponderantly distributed over areas which do not partake in the contact operation proper.

This based upon recognition of the fact that the cathodic coverage of a glow discharge is in its extent dependent upon the pressure in thedischarge vessel. This efiect which is as such known is in the above described contact arrangement in very particular manner utilized, namely, so that the cathodic coverage is by pressure reduction displaced or shifted to areas which are not effected by the contact operation proper. The result is that the specific current load is during the switching operation reduced, by the increase of the cathodic coverage, whereby the cathode vaporization is weakened, and that the contact destruction effected by the cathode vaporization is shifted away from the area of the contact points proper. This latter effect is of particular importance because it largely avoids the deposit of vaporization products on the contact points, therewith also largely avoiding migration of the material.

The above described adjustment of the pressure in the hermetically sealed space supports the effect of highmelting metal formed on the contact springs.

The pressure in the hermetically sealed chamber can be reduced with respect to the atmospheric pressure so as to produce a cathodic coverage which involves the contacts to the extent to which they are provided with the highmeltingmetal. There would in such case result a cathodic coverage corresponding to the extent of the contact areas 4 in FIG. 1. It is, however, also possible, by the use of appropriate pressure, to achieve a cathodic coverage extending beyond the highmelting metal. There will result in this case a still lower current density requiring, however, toleration of some residual cathode vaporization at areas which are not provided with highmelting metal. This is however immaterial because the resultant cathode vaporization is of little importance due to the low specific total current loading. Generally speaking, a compromise will be entered between the area of the surface formed by the highmelting metal and the pressure, considering thereby the energy which is to be controlled by the switching operation to be effected by the contact arrangement involved. In such compromise, the most favorable conditions are to be selected for the corresponding current strength.

Changes may be made within the scope and spirit of the d. appended claims which define what is believed to be new and desired to have protected by Letters Patent.

We claim:

1. A contact arrangement comprising two mutually cooperating contact members disposed within a hermetically sealed chamber which contains a protective gas, said contact members having respective engageable contactmaking areas, a thin sheet of a high melting-metal, selected from the class of metals consisting of molybdenum, tantalum and tungsten, applied to the contact-making area of each contact member, each sheet having an area considerably greater than the contact-making area of the associated contact member, the inert gas filling having a pressure which is with respect to the atmospheric pressure reduced so that the cathodic coverage of a glow discharge extends over an area which is considerably greater than the contact-making area occupied by the contacting surfaces of said contact member, each of said thin sheets having an area of a size to accommodate the extended glow discharge, the cathode vaporization caused by the glow discharge being thereby shifted predominately to areas of said highmelting metal sheets which do not form the actual contact-making areas of the contact members.

2. A contact structure according to claim 1, wherein said highmelting metal is provided on said contact means in the form of applied foils.

3. A contact structure according to claim 1, wherein said highmelting metal is riveted on said contact means.

References Cited by the Examiner UNITED STATES PATENTS 1,089,907 3/14 Coolidge 200166 1,900,256 3/33 Payette 200166 2,200,443 5/40 Dench 313-l46 X 2,321,910 6/43 Hays 313 -146 X 2,323,702 7/43 Berkey -a 200144 2,5 06,414 5/50 Ellwood 20087 2,625,622 1/53 Rixton 200113' 3,007,855 11/61 Ellwood 20087 BERNARD A. GILHEANY, Primary Examiner.

RALPH G. NILSON, MAX L. LEVY, Examiners. 

1. A CONTACT ARRANGEMENT COMPRISING TWO MUTUALLY COOPERATING CONTACT MEMBERS DISPOSED WITHIN A HERMETICALLY SEALED CHAMBER WHICH CONTAINS A PROTECTIVE GAS, SAID CONTACT MEMBERS HAVING RESPECTIVE ENGAGEABLE CONTACTMAKING AREAS, A THIN SHEET OF A HIGH MELTING-METAL SELECTED FROM THE CLASS OF METALS CONSISTING OF MOLYBDENUM TANTALUM AND TUNGSTEN, APPLIED TO THE CONTACT-MAKING AREA OF EACH CONTACT MEMBER, EACH SHEET HAVING A AREA CONSIDERABLY GREATER THAN THE CONTACT-MAKING AREA OF THE ASSOCIATED CONTACT MEMBER, THE INERT GAS FILLING HAVING A PRESSURE WHICH IS WITH RESPECT TO THE ATMOSPHERIC PRESSURE REDUCED SO THAT THE CATHODIC COVERAGE OF A GLOW DISCHARGE EXTENDS OVER AN AREA WHICH IS CONSIDERABLY GREATR THAN THE CONTACT-MAKING AREA OCCUPIED BY THE CONTACTING SURFACES OF SAID CONTACT MEMBER, EACH OF SAID THIN SHEETS HAVING AN AREA OF A SIZE TO ACCOMMODATE THE EXTENDED GLOW DISCHARGE THE CATHODE VAPORIZATION CAUSED BY THE GLOW DISCHARGE BEING THEREBY SHIFTED PREDOMINATELY TO AREA OF SID HIGHMELTING METAL SHEETS WHICH DO NOT FORM AN ACTUAL CONTACT-MAKING AREAS OF THE CONTACT MEMBERS. 